Microbial decontamination of porous model food powders by Vacuum-Steam-Vacuum treatment

The objective of this work was to study the systematic inactivation of immobilized heat-resistant, validated wild-type bacteria (sporulated Bacillus subtilis D2 and vegetative Cronobacter sakazakii H30) in porous enlarged model food powder particles using the Vacuum-Steam-Vacuum (VSV) process. Developed bacterial sensors allowed a local contamination of model particles at a defined intraparticle position. Contradicting previous studies, a spore inactivation of 4 log ₁₀ CFU in high depths of up to 10 mm (particle core) was possible by VSV treatment despite a noticeable intraparticle attenuation. To mimic inactivation in smaller food powder particles, similar-sized bacterial sensors were treated and showed slightly curve-linear kinetics explained by a short warm-up phase (lag time). Measured inactivation was lower than that predicted by traditional capillary (z = 8.0  ^∘ C) treatment of suspensions due to non-linearity in the high temperature regime. This could be described by twice as high z values of 15.4 °C (no lag time) and 17.2 °C (lag time), respectively.Industrial relevance of present workThe emerging Vacuum-Steam-Vacuum (VSV) decontamination process aims at efficient heat transfer on solid surfaces and pores using saturated steam as the heat-transferring fluid. VSV was already used for treating vegetables, fruits, meats and spices. This work describes use of VSV for dry porous solids.